Smokeless biomass pyrolysis with utilization of biochar as a soil amendment is a potentially significant approach for renewable energy production and for carbon sequestration at giga tons of carbon (GtC) scales. The central idea is that biochar (FIG. 1, left), if produced cleanly and sustainably by pyrolysis of biomass wastes and used as a soil amendment, would “lock up” biomass carbon in a form that can persist in soils for hundreds to thousands of years; and at the same time, help to retain nutrients in soils and reduce the runoff of agricultural chemicals.
The capacity of carbon sequestration by application of biochar fertilizer in soils could be quite significant since the technology could potentially be applied in many land areas including croplands, grasslands and also a fraction of forest lands. The maximum capacity of carbon sequestration through biochar soil amendment in croplands alone is estimated to be about 428 GtC for the world. This capacity is estimated according to: (a) the maximal amount of biochar carbon that could be cumulatively placed into soil while still beneficial to soil environment and plant growth; and (b) the arable land area that the technology could potentially be applied through biochar agricultural practice.
Globally, each year about 6.6 gigatons (Gt) of dry matter waste biomass (e.g., crop stovers, dead leaves, waste woods, and rice straws) are produced. Deployment of an advanced biomass pyrolysis technology could turn this type of waste into valuable biochar, bio-syngas, and biofuel products in a distributed manner. Worldwide, this approach could result in a net reduction of greenhouse-gas emissions by about 1.8 Gt of CO2—C equivalent emissions per year, which is about 12% of the current global anthropogenic emissions. Advanced biomass pyrolysis coupled with biochar soil amendment is unique among carbon sequestration strategies in that it can simultaneously offset gigatons of CO2 emissions and build sustainability into agricultural systems. This is a unique “carbon-negative” bioenergy system approach, which on a life-cycle basis could not only reduce but also reverse human effects on climate change.
More scientific and technological development is needed before this approach can be considered for widespread commercial implementation. For example, a new generation of high-tech biochar materials with higher cation change capacity to retain soil nutrients is needed to serve as an effective soil amendment and carbon sequestration agent. Furthermore, biochar occasionally shows inhibitory effects on plant growth (Rondon et al., Biol. Fertil. Soils 43:699-708 (2007); Rillig et al., Applied Soil Ecology 45:238-242 (2010); Gundale, Thomas, DeLuca, Biol. Fertil. Soils 43:303-311(2007)). Organic species including possibly inhibitory and benign (or stimulatory) chemicals are produced as part of the biomass pyrolysis process. A number of organic compounds belonging to various chemical classes, including n-alkanoic acids, hydroxyl and acetoxy acids, benzoic acids, diols, triols, and phenols were recently identified in organic solvent extracts of biochar. Some of these biochar chemicals, including polycyclic aromatic hydrocarbons (PAHs), are potentially phytotoxic or biocidal, especially at high concentrations. More recently, using the techniques of electrospray ionization (ESI) coupled to Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR-MS) with Kendrick mass defect analysis, it has also been determined that the most likely biochar toxin species contain carboxyl and hydroxyl homologous series and that the phytotoxicity of biochar substances is most likely due to degraded lignin-like species rich in oxygen containing functionalities, which is also part of the PAHs type of organic molecules (Smith et al., Environ. Sci. Technol. 47:13294-13302 (2013)). In addition, certain PAHs are suspected carcinogens. If biochar were to be globally used as a soil amendment and carbon sequestration agent at GtC scales, the release of potentially toxic compounds into soil and associated hydrologic systems might have unpredictable negative consequences in the environment. Therefore, it is essential to address some of these undesirable effects in order for biochar to be used as a soil amendment and carbon sequestration agent at gigaton scales. Any new technology that could produce an advanced biochar product that has high cation exchange capacity without any undesirable side effects would be highly desirable for this major mission of using biochar soil carbon sequestration to control climate change towards sustainability on Earth. Recently, a novel method of creating carboxylated biochars was disclosed in International Patent Application No. PCT/US2014/027170 for “Carboxylated Biochar Compositions And Methods Of Making And Using The Same”, which published as International Patent Application Publication Number: WO2014152291A1.